my psp has system software 7.50!!! WTF?? help me plz

i bought this psp from thailand with my friend..he bought one and i bought one. the system software is 7.50 i know that actually that dont excist. but it says right here system software 7.50
my friend didnt do shit. no upgrades neither any downgrades.
he says he just installed fastloader..and his downloaded games work.
i've downloaded marvel ultimate alliance from torrentspy.com the file names are for example dfc-muae.001, 002 and so on. i opend the files with winrar..and suddenly it all became ziped and named dfc-muae.iso and the file size is 1.65 G, so it gotta be right..how do i put that onto my mem stick..so i can play..PLZ HELP ME. my email is full_51190prosent_power@hotmail.com plzzz help me.